As energy costs, both economic and environmental, continue to rise, it is important to look for opportunities to conserve energy. Fortunately, there are numerous opportunities available to work with your utility to help reduce energy costs by increasing energy efficiency. In this article, energy efficiency opportunities for two industrial sectors (metal casting and chemical manufacturing) are highlighted. Minnesota’s manufacturers can evaluate these opportunities to take steps toward becoming more energy efficient. The opportunities in this article were identified through recent studies (see Industrial Energy Study box, left).
Metal Casting
Metal casting facilities commonly engage in smelting and refining ferrous and non-ferrous metals from ore or scrap feedstock and also process metals by casting or otherwise forming various manufactured metal products. Energy use is significant in metal casting facilities. The entire metal casting industrial sector uses energy in processes such as melting, alloying, heating, and producing metal products.
Through MnTAP’s research, conservation opportunities have been identified for aluminum operations and iron operations. However, the sector has some significant process similarities that make the following energy conservation opportunities applicable across the entire sector.
Melting Systems
Melting and molten metal holding technologies comprise a large portion of energy consumption in the primary metals industry. Different types of melting furnaces have differing degrees of efficiency that affect the degree of metal loss and thermal efficiencies.
Electric melting has some overall advantages in higher thermal efficiencies and in lower metal melt loss. Combustion inefficiencies, exhaust waste heat loss, and combustion and oxidation contaminants in the form of dross and slag metal melt loss can contribute to fuel-fired furnace inefficiencies and missed opportunities for thermal recovery. Nonetheless, fuel-fired furnace equipment operations can effectively employ a variety of procedures and methodologies that can lead to some significant energy savings estimates. Additional fuel-fired melting system opportunities includes:
- Insulation integrity and maintenance
- Proper metal furnace charging and fluxing procedures
- Process flow optimization
- Ladle preheating
- Burner tuning
- Furnace and ladle covers
- Waste heat recovery technologies like recuperative and regenerative heat exchangers or combined heat and power applications
Computer Modeling
An industry-led effort to use computer modeling to improve the efficiency of the primary metals casting process is currently underway. Computer models optimize the design of the product configuration so little excess metal is needed and the design accounts for metal flow peculiarities that can result in part defects, hence wasted energy and scrap. Optimized production benefits energy optimization.
Chemical Manufacturing
In general, facilities engaged in chemical manufacturing in Minnesota produce ethanol or manufacture pharmaceuticals, resins, abrasives, perfumes/cosmetics, agricultural chemicals, adhesives, organic dyes, or surface cleaning products. Although the finished products may differ within this sector, sub-sectors identified through this study have significant needs for process heating and emissions control and destruction.
Specific opportunities were identified for ethanol facilities, pharmaceutical manufacturers, and resin manufacturers. However, there are a number of common energy conservation opportunities for many chemical manufacturers.
Process Controls
A significant opportunity for energy conservation is process control optimization. If plants are manually controlled, it is common practice to be operated well within the company’s product specifications. Chemicals can be over-processed, resulting in increased time and energy required to manufacture the product. Automating simple tasks can yield significant energy savings because process operators are less effective at routine control tasks than a control system is. Another process control issue involves scheduling and shut down of equipment which is not being used or idle for long periods of time. It is estimated that improving process controls could save 2 to 4% of electrical energy use.
Thermal Oxidizers
Upgrading thermal oxidizers in chemical manufacturing facilities can result in reductions of fuel use. Such improvements include installing a new burner and valves, refurbishing insulation, and installing an automatic burner management system to maintain efficient combustion. When upgrading, regenerative thermal oxidizers are more efficient than recuperative thermal oxidizers and should be evaluated. Additionally, recuperative catalytic oxidizers and regenerative catalytic oxidizers can further reduce fuel use. Retrofitting thermal oxidizers to include a catalytic system lowers the operating temperature and reduces fuel use up to 50%.
Boiler Upgrades
Similarly, boiler upgrades such as installing new or refurbished burners, O2 trim control, and a burner management system can decrease fuel energy use. Installing a heat recovery system is another option. Such systems pull excess heat from anywhere there is heat: a thermal oxidizer, boiler exhaust, burner exhaust, dryers, or even cooling towers. Energy efficient burners should be able to maintain a stable flame at low oxygen levels throughout the firing range.
Combined Heat and Power (CHP)
CHP provides an opportunity for a number of facilities looking to reduce overall energy consumption. This technology generates electricity on-site and recovers waste heat from the electrical generation for production. Using CHP to produce electricity on-site can result in 80% efficiency while using relatively little additional fuel over current thermal demand.
Conservation Opportunities for Both Sectors
Improvements to process motors, pumps, and fans, as well as compressed air systems can lead to energy savings for both chemical manufacturers and metal casting facilities.
Process Pumps, Fans, and Motors
Many chemical manufacturing facilities have makeup air and ventilation systems in place to comply with a safe workplace environment and to control emissions of dust and other air contaminants. Several resources discuss the evaluation and proper sizing of pumps, fans, and electric motors. The Industrial Technologies Program within the Energy Efficiency and Renewable Energy Office at the Department of Energy has sourcebooks available that discuss efficient design factors such as variable frequency drives and maintenance suggestions. Improvements to pump, fan, and motor components could conserve up to 8% of electrical energy use.
Compressed Air Systems
Compressed air systems can account for up to 25% of electrical energy use. There are a number of common energy conservation opportunities for any compressed air system. These opportunities include:
- Leak identification and repair
- Pressure reduction
- Control multi-compressor system operation
- Reduce or eliminate inappropriate uses
- Reduce or eliminate humidity performance problems
- Increase receiver storage capacity
- Waste heat utilization
More costly solutions include sequencing and flow controls, variable speed compressors to handle variable loads, and proper sizing and distribution of the compressed air system. Depending on system complexity, compressor system energy efficiency can be improved by as much as 20-50%.
Moving Forward
The industrial sector analysis work is one step MnTAP and numerous utilities in Minnesota are taking to provide energy efficiency assistance to industrial users. MnTAP can provide additional resources on the opportunities identified in this article to help save money and improve the environment.
